Characterization of hot pressed Al2O3-platelet reinforced hydroxyapatite composites

Hydroxyapatite reinforced with monocrystalline Al2O3 platelets was densified by hot pressing. The effect of volume fraction and size of platelets on the microstructure, strength and toughness was investigated. It was demonstrated that no phase degradation occurred during thermal treatments. A better homogeneity of composite mixtures was achieved when large platelets had been used. In return, the incorporation of small platelets appeared more favorable to increase the mechanical characteristics, limiting the effect induced by microstructural defects. The flexural strength can reach 140 MPa with an associated fracture toughness of 2.5 MPa sq rt m compared to 137 MPa and 1.2 MPa sq rt m for dense monolithic HAP. The observation of crack propagation allowed us to point out the mechanisms responsible for this toughening. Crack deflection on disk faces should be considered as the initiating phenomenon leading to platelet debonding, crack bridging, or branching. Crack deflection and branching may also result in the formation of unbroken ligaments of material which bridge the crack. (Author)